If you really want to backup the phone which has bootloop issue, put your phone into a freezer with a ziploc bag and wait 5 mins. You may have a chance to turn your phone on and stay running for 10 mins, which is enough for backup process.
I have used this method and sucessfully backup everything. I did not invent this method, just google it and you will see there are a lot people sharing their success story.
The theory behind this is to shrink the microcrack of the soldering joint and make the flux flow again.
Before sending your phone for repair, make sure you take a picture of the water damage sensor, it is right next to the battery connector. If it is pink or red, you can forget sending the phone for repair.
There should be no damage to the phone by putting it into freezer. I send my phone back for repair and they examine it and do not blame me anything. And I got full store credit back for the phone after 8 months of use.
The date on battery is for the battery and not for the phone.
That whole "15 months" thing is an urban legend that came from out of nowhere.
Very simple. All you have to do is take out the battery and look at the label, AND YOU'LL SEE THE DATE.
The manufacture date of the phone is on the serial number. And first digit indicate the year, second and third digit indicate the month. My battery and my phone has 4 months difference in manufacture date.
LG provide warranty for
1. 12 months within date of purchase or
2. 15 months within manufacture date.
It state clear when you sign up the repair, you can also confirm it with LG customer service through their live chat.